treewide: use boost::lround when std::round is unavailable

This is the case with uClibc-ng currently.

Signed-off-by: Rosen Penev <rosenp@gmail.com>
(cherry picked from commit 769cd0ee9f0cf8ceb026aa751b5d4a390bb5dbdc)
(changed define to match master)

src/player/CrossFade.cxx

@@ -23,10 +23,9 @@
 #include "AudioFormat.hxx"
 #include "util/NumberParser.hxx"
 #include "util/Domain.hxx"
+#include "util/Math.hxx"
 #include "Log.hxx"
 
-#include <cmath>
-
 #include <assert.h>
 
 static constexpr Domain cross_fade_domain("cross_fade");
@@ -112,7 +111,7 @@ CrossFadeSettings::Calculate(SignedSongTime total_time,
 
 	if (mixramp_delay <= FloatDuration::zero() ||
 	    !mixramp_start || !mixramp_prev_end) {
-		chunks = std::lround(duration / chunk_duration);
+		chunks = lround(duration / chunk_duration);
 	} else {
 		/* Calculate mixramp overlap. */
 		const auto mixramp_overlap_current =